It is now commonplace to provide a disposable diagnostic device for the analysis of a single analyte or multiple analytes that originate from a liquid biological sample. Examples of such devices include pregnancy tests and glucose meters for diabetics. In the case of a typical pregnancy test, urine is applied to a wick or collection zone, upon which the sample interacts and mixes with an antibody, or antibodies that specifically recognise the analyte of interest. One of the aforementioned antibodies is always coupled to a colourmetric indicator (often a gold sol or latex particle) for the visual interpretation of a result and often considered as the primary antibody.
The sample and the released components pass through the associated materials (often nitrocellulose) in a lateral flow manner. Deposited on to the nitrocellulose are two zones (or lines) of capture molecules. The first zone (or line) is often the second antibody of a pair that detects the presence of the analyte of interest, however in some embodiments this line is composed of avidin or streptavidin that binds to a biotin coupled to antibody. The second line is often deemed as a control line, and comprises an antibody that specifically recognises the primary antibody or a component bound to the surface of the colourmetric indicator.
The intensity of the first line of the two mentioned above is proportional to the quantity of analyte of interest present in the biological sample. This is deemed as the test line. The second line is used to confirm whether the test has operated correctly, by releasing the reagents, and fluid migrating appropriately. Together the lines represent the manner through which data can be extracted from the immobilised immunoassay that takes place within the device.
In purely visual (i.e. human eye dependent) test devices, a non-skilled user can be confused when a positive result is weak, it could be missed by the user, and considered as a negative, or provide the user with an ambiguous result leading to uncertainty. This may lead to inappropriate conclusions.
It would therefore be desirable to provide an automated, preferably electronic, detector system whereby the risk of inaccuracy can be reduced in terms of determining more reliably, whether there is sufficient contrast (colour change) between a test or control line zone and background and also, to ensure that the line intensities are read/interpreted at the appropriate time post sample application.
Furthermore, our unpublished co-pending application GB0603665.1 discloses the detection of active protease enzyme using a modified lateral flow immunoassay.
U.S. Pat. No. 4,791,461 discloses a portable analysis device comprising a housing and an optical system consisting of a light source and a photodetector. One or more test elements are mounted on a support strip and are used to perform an assay on a sample. The support is then placed in the housing and is caused to move relative to the housing and the optical system so that the photodetector produces a change in output signal indicative of the reaction of at least one of the test elements in response to the presence of a predetermined analyte in the sample.